- See Original Sin for the "First Sin".
The Chantry holds that in -395 Ancient seven Magisters Sidereal, each a High Priest to one of the Old Gods, physically entered the Golden City. They did so at the behest of their gods to open "the unreachable gate" in exchange for "power and glory beyond all reckoning". Reputedly the spell required two-thirds of the lyrium in the Tevinter Imperium as well as the blood of several hundred slaves. But instead of the dragons the mages found the Maker himself upon the throne of heaven. The City turned black and the magisters were cast out as the first darkspawn, inadvertently causing the First Blight.
While the Orlesian Chantry insists that a flaw inherent to human nature led to mankind's corruption, Tevinter authors lay the blame squarely on the Old Gods. They also claim that the darkspawn always existed, and that the Blight and magisters are not even related. 
Accounts of the survivors
Corypheus, one of the seven magisters and the High Priest of Dumat tells that he breached the Fade and walked the halls of the "Golden City". Prior to the event Corypheus had been secretly discussing how to reverse the weakening religious influence of Old God worship with the other priests. Corypheus states that they "sought the golden light" and Dumat "offered the power of the gods themselves". He also says that he wanted "to serve the Old Gods of the empire in person".At midnight Corypheus sacrificed his elven servants in a blood magic ritual at the great altar, the "Claw of Dumat". But the city that was "supposed to be golden" and "theirs" was black and corrupt instead, and he knew "darkness ever since". Corypheus emphasizes that he "found only chaos and corruption, dead whispers" and that he "had seen the throne of the gods, and it was empty". Cole can sense that Corypheus feels betrayed. In his later private recollections, Corypheus rejects the accusation that they "brought darkness into the world", asserting that they "discovered the darkness", "claimed it as their own, let it permeate their being". The fate of other magisters is unknown to Corypheus, yet at least some of them survived, including the Architect
- Dragon Age: The World of Thedas, vol. 1, p. 114
- Dragon Age: The World of Thedas, vol. 2, p. 54
- Canticle of Silence 1:16, Dragon Age: The World of Thedas Volume 2 p.57
- Codex entry: The Cardinal Rules of Magic
- Canticle of Silence 3:2, Dragon Age: The World of Thedas Volume 2 p.58
- Codex entry: The Chant of Light: The Blight
- Codex entry: Corypheus
- Codex entry: In Hushed Whispers
- In a dialogue with Dorian Pavus after reaching Skyhold.
- According to Corypheus in Dragon Age: Inquisition during In Your Heart Shall Burn and Doom Upon All the World.
- According to the memories of Corypheus' servant.
- According to Corypheus in Dragon Age 2 Legacy DLC
- Dialogue between Cole and Dorian
- Corypheus's Memories
- Codex entry: A Different Darkspawn?
- Chatting With David Gaider.